I have to admit if I get no nod/wave/acknowledgement back on a calm stretch of road I mutter the words "miserable bastid" quite a lot, I swear when riding quite a bit though, usually "oh ****!"
It does seem to be the weekends mostly where nodding is lost, must be all those part timers who don't know better yet....I like the notion of belonging to a like minded group who love to ride and all that jazz
I stopped nodding to Harley/Cruiser riders for a while though, I had one cheeky f**k shake he head at me in reply to a nod....I wasn't good enough for him and his overly chromed up, over weight, under performing, last century bike...